Parathyroid hormone-related peptide (PTHrP) plays a major role in chondrocyte maturation, and thereby, skeletal development. Targeted disruption of the PTHrP gene in mice causes accelerated chondrocyte maturation, while a constitutively active mutant PTH/PTHrP receptor, or targeted overexpression of PTHrP to differentiating chondrocytes, causes marked delays in chondrocyte maturation and skeletal development. Little is known about the mechanism by which PTHrP regulates the maturation of growth plate chondrocytes. PTHrP increases the expression of Bcl-2 in chondrocytes, preventing apoptosis, and deletion of the gene encoding Bcl-2 leads to accelerated maturation of chondrocytes and shortening of long bones. Thus, Bcl-2 may lie downstream of PTHrP in the control of chondrocyte maturation and skeletal development. The goal of the present proposal is to determine whether regulation of Bcl-2 in chondrocytes is a mechanism by which PTHrP regulates growth plate maturation and skeletal development, and to determine the molecular mechanisms by which PTHrP regulates Bcl-2 expression. The Specific Aims are to: (1) use a genetic complementation approach to further establish and define the role of Bcl-2 downstream of PTHrP in regulating chondrocyte maturation in the growth plate; (2) elucidate the signal transduction mechanisms involved in the chondrocyte-specific regulation of Bcl-2 expression by PTHrP and determine whether the regulation of Bcl-2 is transcriptional or not; and (3) determine whether other molecules known to affect chondrocyte maturation (Ihh, the FGFs, and the BMPs) affect Bcl-2 expression and whether they intervene between PTHrP and Bcl-2 on the same signalling pathway. It is suggested, by the applicant, that the information obtained in this study will provide important insights into the molecular mechanisms that underlie normal skeletal development and whose disruption can result in skeletal deformities, on the one hand, and the generation of chondrogenic tumors on the other.